In the United States high-tech goals are becoming precise. In a recently issued report (see report summary in Chem. Eng. News, 62, no. 29, July 16, 1984, pp. 22-24), entitled "The Engineering Mission of NSF Over the Next Decade," a National Science Board panel suggested as one of fifteen areas of focus for engineering centers of excellence:
"Membrane research for such areas as water desalination, gas separation, metal recovery, water purification, packaging, kidney dialysis, artificial pancreas, and drug release control."
Membrane research has been ongoing since the early 1900's. For example, binding of enzymes to suitable insoluble substrates to render the resultant product commercially useful is known. Such immobilization techniques for microbial cells and enzymes have been classified into three methods: carrier binding method, cross-linking method, and trapping method by I. Chibata in "Basic Biology of New Developments in Biotechnology", A. Hollaender et al., editors, Plenum Press, N.Y., 1983, pp. 465-496. Chibata (supra, at p. 469) has cautioned that these immobilizations should be carried out under very mild conditions to avoid the inactivation of enzymes. It is known that living cells, which contain such enzymes, are even more sensitive than the enzymes, because the conditions that destroy the efficacy of the enzyme will cause the death of the living cell even more easily.
Membrane technology is reviewed by D. C. Warren in "New Frontiers in Membrane Technology and Chromatography: Applications for Biotechnology", Analytical Chemistry, 56, No. 14, December 1984, pages 1529A-1544A.
It is also known in the art to immobilize living cells encased in continuous domains such as alginic acid and polymers. Enzymes adsorbed onto inorganic particulates and then dispersed throughout the interstices of a network of interconnected, interwoven fibers of PTFE (fibrilated PTFE) have been described in U.S. Pat. No. 3,766,013. This patent further teaches that particulate material modified by surface adsorption of enzymes can be mixed with PTFE and the mixture fibrillated into a coherent mass. The ability to fibrilate polytetrafluoroethylene emulsion and mix particulate material with it and then convert the product to a porous sheet has been described in U.S. Pat. No. 4,194,040, and methods for making such fibrillated polymers have been reported in U.S. Pat. Nos. 3,864,124 and 4,153,661. Recently, enthusiasm for immobilizing enzymes has been summarized by T. H. Maugh II in "A Renewed Interest in Immobilized Enzymes", Science, 223, 474-476 (1984).
Immobilization of microorganisms on supports such as agar, alginate, carrageenan, cellulose, polyacrylate, and polyamide has been described by S. Birnbaum, P. Larson, and K. Mosbach in "Solid Phase Biochemistry," W. H. Scouten, Ed., Wiley, 1983, vol. 66, chapter 15. U.S. Pat. No. 4,434,231 describes processes for embedding microorganisms within a matrix of a polymer gel, and U.S. Pat. No. 4,452,892 teaches immobilization of biologically active material in a hydrogel on a support.
U.S. Pat. No. 4,456,685 discloses polyurethane foams to which are bound aspartase-producing microorganisms.
Confining microbials to one side of a membrane filter in a dialyzer has been reported by W-W Tso and W-P Fung, Biotechnol. Lett., 3, 421 (1981) and microbial cells immobilized in a collagen membrane, which was placed over the Teflon.RTM. membrane of an oxygen electrode, was described by R. K. Kobos, Trends in Analytical Chemistry, 2, 143 (1983).